Insights into the effect of bromine‐based organic salts on the efficiency and stability of wide bandgap perovskite

Abstract Wide bandgap perovskite solar cells (WB‐PSCs) sustained serious deficit of open‐circuit voltage (VOC) and instability in the development process, which limited the full play of their advantages, especially in tandem solar cells. Surface passivation engineering of alkyl amine halide salts has been used extensively to improve the performance of PSCs. Here, the photovoltaic performance of FA0.83Cs0.17 Pb(I0.8Br0.2)3 WB‐PSCs based on methyl bromide (MABr) and bromide guanidine (GABr) passivation was systematically investigated. It was proved that both MABr and GABr significantly passivate the defects, resulting in lower trap density. Eventually, the efficiency arrives at 18.6% based on MABr‐treated perovskite film, and an improved VOC up to 1.235 V was obtained with a VOC‐deficit of only 415 mV, which is one of the highest value for the PSCs with 1.65 eV bandgap. It is noted that the devices treated with MABr exhibited enhanced moisture stability than that of the reference and GABr treated. X‐Ray Diffraction (XRD) revealed that GABr is likely to cause severer phase transition to δ‐phase nonperovskite. This paper provides an important insight to surface passivation strategies, both performance and stability in devices need to be considered simultaneously.